The disruption of various components of the pathway controlling E2F accumulation, either the activation of positive acting components such as Ras, Myc and G1 cyclins, or the inactivation of negative components such as Rb and the GDK inhibitors, can lead to the loss of cell growth control underlying the development of various forms of human cancer. Mammalian E2F is composed of a family of heterodimeric proteins encoded by distinct genes. Given the importance of E2F in the control of proliferation and apoptosis, it is critical that we understand the mechanisms regulating the activity of each E2F family member and physiological consequences of such regulation. The proposed studies will be directed at understanding the role and the mechanism of action of E2F1, E2F2 and E2F3 in the regulation of cell death, and how other signal transduction pathways important for normal cellular proliferation may intersect and modulate E2F- mediated apoptotic signals. These studies will employ both tissue culture and mouse models, where each of these genes have been specifically disrupted, in order to determine specific roles for these E2F activities in the control of apoptosis. These studies will involve four specific aims: 1) the identification of specific genes regulated by E2F1, E2F2 and E2F3 in part by using SAGE (Serial Analysis of Gene Expression) and GEA (Gene Expression Array) technology. 2) an investigation of the mechanism underlying the role of E2F1 as a mediator of apoptosis that will include the determination of the relative contributions of different protein domains in eliciting an apoptotic response. 3) an investigation into the potential role of E2F1 as a normal growth checkpoint that would ensure aberrantly proliferating cells to commit to a cell suicide pathway. 4) a molecular analysis of how cell survival pathways, activated upon normal cell growth, counter an E2F mediated apoptotic signal. These studies will further our understanding of the individual contributions of the different E2F family members towards the control of apoptosis, and how the E2F transcriptional program is normally coordinated with other signal transduction pathways during normal or deregulated cellular proliferation.